JP3982780B2 - Method for manufacturing forged thin-walled casing made of magnesium alloy - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnesium alloy, and more particularly to a forged thin-walled casing and a method for manufacturing the same.
[0002]
[Prior art]
Magnesium has the smallest specific gravity among metal materials currently in practical use, and magnesium is 1.8 as compared with 2.7 of aluminum, and is expected as a light weight material and is becoming popular. Most magnesium alloys are used as castings. In addition to the main element magnesium, the alloy elements of the magnesium alloy include the basic elements aluminum and zinc to obtain strength and castability, as well as zirconium to provide strength and toughness, and rare earth elements and silver to provide heat resistance. . Magnesium alloys are widely used in aerospace equipment parts, nuclear coating materials, ground transportation equipment, cargo handling equipment, industrial machinery / tools, electrical / communication equipment, agriculture / forestry / mining machinery, office equipment, optical equipment, sports equipment, etc. It's being used.
[0003]
As a prior art, for example, Japanese Patent Application Laid-Open No. 6-172949 discloses a magnesium alloy member in which a member such as an automobile wheel is made of a magnesium alloy and a method for manufacturing the same. That is, according to the disclosed method for producing a magnesium alloy member, “(1) Magnesium alloy casting material is forged and formed into a member having an average crystal grain size of 100 μm or less, and then subjected to T6 heat treatment (solution treatment and artificial treatment). (2) Set the forging temperature within the range of 300 to 420 ° C. (3) Set the magnesium alloy member to the automobile wheel.
Further, the magnesium alloy member is “a magnesium alloy member formed by performing T6 heat treatment (solution treatment and artificial aging treatment) after casting forging, and at least the surface portion of the member is made of 6-12 aluminum. It contains a weight percentage and has an eutectic structure of an intermetallic compound of magnesium and aluminum and an α phase during the T6 heat treatment (solution treatment and artificial aging treatment), and an average crystal grain size is increased by plastic working during the forging. A magnesium alloy member in which the eutectic composition is 200 μm or less and dispersed in a chain form. ”
[0004]
As for the magnesium alloy, a technique in which a molded product obtained by high-pressure casting a molten magnesium alloy is subjected to T6 heat treatment (solution treatment and artificial aging treatment) or a so-called cast forging method in which a cast product is forged.
Recently, a new molding method using an injection molding method has attracted attention as a semi-melt molding method performed in a solid-liquid coexistence region. Molded products obtained by this molding method have no dendrites found in general cast products, a fine structure is obtained, and there are fewer pores and higher density than molded products obtained by the die casting method. It is attracting attention because it can be heat-treated, and research and development is underway in various areas.
[0005]
[Problems to be solved by the invention]
However, the technique disclosed in Japanese Patent Laid-Open No. Hei 6-172949 is intended for large parts such as automobile wheels, and requires considerable equipment costs to produce, and T6 heat treatment (solution treatment). The treatment and artificial aging treatment) have a problem of requiring a long time.
Further, a magnesium alloy molded product produced by a semi-melt forming method may have casting defects or oxides inside and on the surface during the manufacturing process. If these are present, the corrosion resistance of the plated surface cannot be improved even if the component surface is plated, and the commercial value as viewed from the outside is also reduced. Therefore, measures are taken to improve the corrosion resistance by surface coating. However, in this case, it is difficult to produce a metallic luster and a problem remains in aesthetics.
[0006]
The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a magnesium alloy thin-walled casing that is lightweight and high quality by forging, and a method for manufacturing the same. . The “wall thickness of the main part” in the present invention means a uniform wall thickness that occupies most of the bottom 7 and the side 8 of the housing 6 shown in FIG. However, the protrusion height formed by the predetermined symbol recess 20 is not included, and although there is a local boss or a further locally thin portion not shown, these local bosses and Further local thin wall thickness shall not be taken into account. In addition, the “predetermined symbol” means a symbol such as a character, a number, or a mark formed by protruding from the outer surface by the predetermined symbol recess 20 in FIG.
[0007]
[Means for Solving the Problems]
As a result of various studies on various magnesium alloys in order to solve the above-mentioned problems, the present inventors have found that by weight ratio, Al: 1 to 6%, Zn: 0 to 2%, Mn: 0.5% or less In addition, a magnesium alloy having a composition of trace element 0.2% or less, the balance Mg and inevitable impurities, for example, ASTM standard AM20 alloy and AZ31 alloy has been found to have excellent forgeability, and a plurality of steps of rough forging and finish forging are performed. Invented the magnesium alloy forged thin-walled casing of the present invention and a method for producing the same by forging.
[0009]
The method for producing a forged thin casing made of magnesium alloy according to the present invention is such that the temperature of the magnesium alloy material is 350 to 550 ° C., the mold temperature used for forging is 350 to 450 ° C., and a molding load of 3 to 30 ton / cm 2 is applied. Then, rough forging is performed at a forging speed of 10 to 500 mm / sec, and then the forged molded casing is 300 to 500 ° C., the mold temperature for forging is 300 to 400 ° C., and molding is performed at 1 to 20 ton / cm ² . Finishing forging at a forging rate of 1 to 200 mm / sec while applying a load, the main part is formed into a casing having a thickness of approximately 1.0 mm or less, and trimming and machining are performed on the casing. A special composite anodic oxide film treatment is performed on the entire surface of the housing.
[0011]
Further, the magnesium alloy forged thin-walled housing manufacturing method of the present invention is formed into a rough shape in a rough forging step, and then formed into a curved surface having a small radius at the corner inside the housing in a finish forging step, The bottom and sides of the housing are formed to have a target dimension and thickness, and a predetermined symbol is projected from the outer surface on the outer surface of the housing so as to be integrally formed.
[0012]
The surface of the resulting magnesium alloy forged thin-walled casing is treated with a special composite anodized film to forge magnesium alloy with excellent anti-corrosion properties that cannot be obtained by painting and a metallic luster that makes use of the magnesium alloy substrate. It is a manufacturing method of a thin casing.
[0013]
Moreover, the composition of the magnesium alloy material in the manufacturing method of the forged thin-walled casing made of magnesium alloy is Al: 1 to 6%, Zn: 0 to 2%, Mn: 0.5% or less, trace elements of 0. It is characterized by comprising 2% or less, the balance Mg and inevitable impurities.
[0014]
Hereinafter, the application and reasons for limitation of various conditions according to the present invention will be described.
1) Magnesium alloy material for forging:
When a magnesium alloy material is forged to form a thin casing, the magnesium alloy must be excellent in forgeability. Therefore, a magnesium alloy material consisting of Al: 1 to 6%, Zn: 0 to 2%, Mn: 0.5% or less, trace elements of 0.2% or less, the balance Mg and unavoidable impurities is selected by weight ratio. . If aluminum is low, the forgeability is good, but the rigidity is poor, so at least 1% of aluminum is necessary. As the aluminum content increases, forgeability and corrosion resistance decrease, so the aluminum content is limited to a maximum of 6%. Zinc also has the same effect, and is limited to 0 to 2% because of forgeability and rigidity. For example, ASTM standard AZ31 alloy and AM20 alloy. The trace elements are rare earth elements, lithium, zirconium and the like.
[0015]
2) Heating magnesium alloy material for forging:
When heating the magnesium alloy material in the air, the surface will oxidize and adversely affect the forgeability, corrosion resistance, and appearance, so the magnesium alloy material is heated with an inert gas atmosphere such as argon gas. Perform in a furnace. The heating temperature of the magnesium alloy material is uniformly heated at 350 to 550 ° C. (furnace atmosphere temperature), which is slightly higher than the forging temperature. For example, when the size of the material is 30 mmφ × 10 to 30 mm, the heating time is about 10 to 20 minutes. Moreover, the heating temperature of the coarse-shaped housing | casing before finish forging shall be 300-500 degreeC.
[0016]
3) Forging temperature (temperature of magnesium alloy material during forging):
The temperature of the magnesium alloy material during forging is set to 350 to 550 ° C. If the temperature is lower than 350 ° C., the metal flow of the magnesium alloy during forging (hereinafter referred to as “metal flow”) cannot be obtained smoothly, and it is difficult to reduce the thickness. On the other hand, if the temperature exceeds 550 ° C., the crystal grains become coarse, so 550 ° C. is set as the upper limit temperature. Finish forging is carried out following rough forging, but the temperature of the magnesium alloy material is slightly lower than that during rough forging and is 300 to 500 ° C.
[0017]
4) Mold temperature:
In order to prevent a temperature drop during forging of the magnesium alloy material, the temperature is kept slightly lower than the magnesium alloy material temperature at 350 to 450 ° C. during rough forging and at 300 to 400 ° C. during finish forging. The mold material preferably has a high temperature strength.
[0018]
5) Forging speed:
If the forging speed is too fast, the metal flow is not smoothly performed, while if it is too slow, the productivity is lowered. If the forging speed exceeds 500 mm / second, the metal flow cannot smoothly follow the forging speed, and the metal flow is disturbed. Therefore, the upper limit of the forging speed is set to 500 mm / second. If the forging speed is less than 1 mm / second, the productivity is lowered. Therefore, the lower limit of the forging speed is set to 1 mm / second. In particular, in rough forging that emphasizes productivity, the speed is 10 to 500 mm / second, and in finish forging that emphasizes formability, the speed is 1 to 200 mm / second.
[0019]
6) Molding load:
Particularly in rough forging where importance is placed on productivity, since the load on the product and the mold becomes excessive at a molding load exceeding 30 ton / cm ² , the upper limit of the molding load is set to 30 ton / cm ² . On the other hand, since it becomes difficult to mold at a molding load of less than 1 ton / cm ² , the lower limit of the molding load is set to 1 ton / cm ² . Particularly, rough forging requiring a forming load is 3 to 30 ton / cm ² , and finishing forging which is sufficient even if the forming load is small is set to 1 to ²⁰ ton / cm ² .
[0020]
7) Surface treatment (formation of special composite anodized film):
The oxide film is formed by a special composite anodizing method based on JIS H8651. The liquid is mixed with sodium dichromate, acidic sodium fluoride or acidic potassium fluoride or acidic ammonium fluoride, ammonium nitrate, primary sodium phosphate, aqueous ammonia, etc. according to the magnesium material composition, desired color, etc. Process by temperature, time, current value.
By this special composite anodic oxide film treatment, it is possible to obtain a forged thin-walled casing having excellent corrosion resistance that cannot be obtained by painting and a metallic luster that makes use of the magnesium alloy substrate.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
(Embodiment)
FIG. 1 is a diagram showing the forging process of the present invention. FIG. 2 is a schematic longitudinal sectional view of an upper and lower mold for forging with a forging material placed thereon. FIG. 3 is a schematic side view of the forging machine. In the present invention, as shown in FIG. 1, Al is 1 to 6%, Zn is 0 to 2%, Mn is 0.5% or less, trace element is 0.2% or less, remaining Mg and inevitable Magnesium alloy material made of impurities, such as ASTM standard AZ31 alloy (Al 3%, Zn 1%, etc.) and AM20 alloy (Al 2%, Mn 0.5%, etc.) 30-40mmφ × 10 A forging material having a length of ˜30 mm is placed in an electric heating furnace filled with argon gas and heated uniformly at 350 to 550 ° C. Next, the forging material is taken out from the electric heating furnace, placed on the lower mold 2 shown in FIG. 2, rough forging is performed using the forging machine shown in FIG. 3, and then finishing forging is performed. In FIG. 2, 4 indicates a heater and 5 indicates a thermocouple.
[0022]
As shown in FIG. 3, the forging machine 9 is a mechanical forging machine that applies the rotational force of the flywheel 11, and transmits the force to the connecting rod 12. 3 is detachably connected. The upper die 3 moves in the direction of the arrow L, and a forming load is applied to the forging material 1 placed on the lower die 2 at regular intervals. A mechanical forging machine having a high forging speed is used for the rough forging of the rough shape forming, and a hydraulic forging machine having a relatively low forging speed is used for the final forging for forming the final product dimensions. Reference numeral 10 denotes an eccentric shaft, and 13 denotes a frame.
[0023]
FIG. 4 (rough forging die) and FIG. 5 (finish forging die) show schematic longitudinal sectional views of the embodiment of the die for use in the present invention. The upper die 3 shown in FIG. 4 subjected to rough forging has a convex lower end corner 14 formed with a radius of 2 to 7 mm. In rough forging, a portion formed by forging at the convex lower end corner portion 14 of the upper mold 3 is a corner portion inside the housing 6. In rough forging, the inner corner of the housing 6 is formed to be slightly thick. The thick portions of the bottom portion 7 and the side portion 8 of the casing 6 that are pressed by the two dies 3 and 2 and are forged are formed to have a thickness that is equal to or slightly thicker than the final thickness. Further, as shown in FIG. 4, the lower mold 2 is formed with a concave corner 15 having a radius of 0.5 to 1.5 mm. In rough forging, the forged portion of the concave corner 15 of the lower mold 2 is the outer corner of the housing 6, so it is preferable to form the final shape target dimension from the beginning.
[0024]
Next, as shown in FIG. 5, the upper die 16 used for finish forging is formed with a convex lower end corner 18 having a radius of 0.5 to 1.5 mm. Depending on the shape of the lower end corner 18 of the convex portion, the corner formed into a slightly thick radius of 2 to 7 mm by rough forging is formed to a radius of 0.5 to 1.5 mm, and the two metals shown in FIG. A part of the thick portion of the casing 6 pressed by the dies 3 and 2 and roughly forged to form a metal flow in the recess 20 that is engraved for a predetermined symbol inside the lower die 17 by finish forging. The inner side surface 21 of the bottom 7 of the housing 6 is forged and formed to be flat and have a desired final thickness. The predetermined symbol is formed so as to protrude integrally on the outer surface of the housing 6. A is an example of a case size of 80 mm square. The forging conditions are forging temperature 350 to 550 ° C., mold temperature 350 to 450 ° C., forging speed 10 to 500 mm / second, and molding load 3 to 30 ton / cm ² for rough forging, and forging temperature 300 to The temperature is 500 ° C., the mold temperature is 300 to 400 ° C., the forging speed is 1 to 200 mm / second, and the molding load is 1 to 20 ton / cm ² .
[0025]
In the present invention, a target main part thickness of 0.5 to 1.0 mm can be obtained by rough forging and finish forging under the forging conditions described above. Representative examples from the experiments will be described as examples below.
Example 1
30 to 40 mmφ × 10 to 40 mm long forging magnesium alloy material (10 pieces) Forging temperature (temperature of magnesium alloy material during forging) 500 ° C., mold temperature 400 ° C., forging speed 200 mm / second, molding load 20 ton When rough forging was performed under forging conditions of / cm ² , a main part having a thickness of 0.8 to 1.0 mm was obtained.
Next, as a result of finishing forging under forging conditions of a forging temperature of 400 ° C., a mold temperature of 350 ° C., a forging speed of 50 mm / sec, and a molding load of 10 ton / cm ² , the thickness of the main part is 0.6 to 0 as targeted. It was possible to mold to a thickness in the range of 8 mm.
[0026]
(Example 2)
When rough forging was performed under the same rough forging conditions as in Example 1 except that the mold temperature was 300 ° C., the thickness of the main part was 1.6 mm or more. Next, as a result of finish forging under the same finish forging conditions as in Example 1, the thickness of the main part was 1.5 mm. As described above, when rough forging is performed at a low mold temperature of 300 ° C., heat is taken away by the low-temperature mold and the material temperature is lowered, so that the plastic flow (metal flow) is difficult to be performed. It turned out that thin wall forming is difficult by finish forging.
[0027]
(Example 3)
When rough forging was performed under the same rough forging conditions as in Example 1 except that the forging temperature (temperature of the magnesium alloy material during forging) was 340 ° C. and the forming load was 30 ton / cm ² , the thickness of the main part was 1 It became more than 8mm. Next, as a result of finishing forging under the same finishing forging conditions as in Example 1, the thickness of the main part was 1.6 mm or more.
This is because the material temperature at the time of forging is low, so even if the molding load is increased to 30 ton / cm ² , it is difficult for plastic flow (metal flow), and it is difficult to perform thin-wall molding by finish forging performed thereafter. I found out that
[0028]
(Example 4)
When rough forging was performed under the same rough forging conditions as in Example 1 except that the forging temperature (the temperature of the magnesium alloy material during forging) was 560 ° C. and the mold temperature was 460 ° C., the thickness of the main part was 1. Although it could be molded to 0 mm or less, the plastic flow (metal flow) was intense because the material temperature was too high, and a wavy trace of metal flow remained on the surface. Subsequently, finish forging was performed with various finish forging conditions, but the wavy traces of the metal flow could not be made uniform and flat. From this result, it was confirmed that the forging temperature was not good if it was too high.
[0029]
(Example 5)
When rough forging was performed under the same rough forging conditions as in Example 1 except that the molding load was 0.8 ton / cm ² , the thickness of the main part was 2.0 mm or more. Next, as a result of finishing forging by changing various finishing forging conditions, in particular, by increasing the molding load to 30 ton / cm ² or 40 ton / cm ² , the main part has a thickness of up to 1.0 mm. The thickness was uneven and the moldability was not good.
[0030]
(Example 6)
When rough forging was performed under the same rough forging conditions as in Example 1 except that the forging speed was 500 mm / second, the plastic flow (metal flow) was disturbed, the filling into the mold was poor, and the shape was accurate. Could not be molded. The forging speed was 2.5 mm at 5 mm / second because the pressing time was slow and the temperature of the material was lowered when the forging speed was 10 mm / second or less in rough forging.
[0031]
Since the forged burrs are generated around the upper end of the forged thin-walled casing made of magnesium alloy thus obtained, trimming is performed to remove the forged burrs by punching. Next, the necessary part is machined. Magnesium alloys may oxidize after forging and lose metallic luster, so an oxide film is formed by a special composite anodized film treatment, and the metallic luster that makes use of the excellent corrosion resistance and magnesium alloy base that cannot be obtained by painting A forged thin-walled housing made of magnesium alloy having
[0032]
【The invention's effect】
The magnesium alloy forged thin-walled casing of the present invention is lighter and more rigid than aluminum alloy parts, has a predetermined symbol on its outer surface, and has excellent anticorrosion and special composite anodized film on the entire surface. The metallic luster that makes use of the magnesium alloy base is formed, and its application can be expected as a thin-walled casing for the purpose of reducing the weight of various devices.
[Brief description of the drawings]
FIG. 1 is a process diagram showing a forging operation process of the present invention.
FIG. 2 is a schematic longitudinal sectional view of an upper and lower mold for carrying out forging by placing a forging material according to the present invention.
FIG. 3 is a schematic side view of a forging machine according to the present invention.
FIG. 4 is a schematic longitudinal sectional view of an upper and lower mold used for rough forging according to the present invention.
FIG. 5 is a schematic longitudinal sectional view of upper and lower molds used for finish forging according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Forging material 2 Lower die 3 Upper die 4 Heater 5 Thermocouple 6 Case 7 Case bottom 8 Case side 9 Forging machine 10 Eccentric shaft 11 Flywheel 12 Connecting rod 13 Frame L Forming load direction 14 Convex lower end corner 15 of upper die for rough forging Concave corner 16 of lower die for rough forging Upper die 17 for finish forging Lower die 18 for finish forging Lower end corner of convex portion of upper die for finish forging 19 Concave corner portion 20 of finish forging lower mold 20 Predetermined concave portion 21 Inner side surface of bottom of casing

Claims (4)

The temperature of the magnesium alloy material is set to 350 to 550 ° C., the mold temperature used for forging is set to 350 to 450 ° C., and rough forging is performed at a forging rate of 10 to 500 mm / sec while applying a forming load of 3 to 30 ton / cm ^2. Then, the roughly forged molded casing is 300 to 500 ° C., the mold temperature used for forging is 300 to 400 ° C., and finished at a forging speed of 1 to 200 mm / sec while applying a molding load of 1 to ²⁰ ton / cm ^2. Forming a casing with a main part thickness of approximately 1.0 mm or less by forging , trimming and machining the casing, and then performing a special composite anodic oxide coating on the entire casing A method for producing a forged thin-walled casing made of magnesium alloy. In the rough forging process, a rough shape is formed, and then in the finish forging process, the corners inside the casing are formed into curved surfaces having a small radius, and the bottom and sides of the casing are formed to a target dimension thickness, 2. The method for manufacturing a magnesium alloy forged thin casing according to claim 1 , wherein a predetermined symbol is protruded from the outer surface and integrally formed on the outer surface of the casing. The magnesium alloy forging according to claim 1 or 2 , characterized by having a special composite anodic oxide film treatment, an excellent corrosion resistance that cannot be obtained by coating, and a metallic luster that makes use of the magnesium alloy substrate. A method for manufacturing a thin housing. The composition of the magnesium alloy material consists of Al: 1 to 6%, Zn: 0 to 2%, Mn: 0.5% or less, trace elements of 0.2% or less, the balance Mg and unavoidable impurities. method of manufacturing a magnesium alloy forged thin casing according to any one of claims 1 to 3, characterized in.

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